Certain emission chains are suitable for receiving an input signal, then decomposing it into at least one first and one second signal component which each follow at least in part, in an analog form, a different physical pathway and may possibly undergo different processing operations, before these two signal components thus processed in a parallel manner are combined to provide a signal to be emitted.
The various physical pathways traversed may induce different delays on each of the signal components thus processed in parallel. In addition to these differential delays, the fact that the various signal components follow different physical pathways may generate additional distortions such as for example differences in gain, or differences in phase, or else any other type of distortion, between these various components of the signal to be emitted.
These various potential signal distortions are liable to degrade the characteristics of the signal emitted, such as for example the frequency spectrum of the signal emitted. They are also liable to have an impact on the performance of a suitable receiver for receiving the signal emitted by the emission chain.
FIG. 1 illustrates an example of such an emission chain which comprises a signal decomposition module 101 suitable for receiving a digital input signal 100 provided by a modulator, and for providing, on the one hand, a first signal component 307, corresponding here to an amplitude modulation component (AM) and, on the other hand, a second signal component 308, corresponding to a phase modulation component (PM).
These first and second signal components are respectively processed in parallel. The first and second outputs of the signal decomposition module 101 are linked respectively to two digital analog converters 102 and 103. An output of the digital analog converter 103 is linked to a phase modulator 104. The latter is suitable for modulating an input signal according to a carrier frequency.
This emission chain comprises a power amplifier 105 which is suitable for receiving, on the one hand, on a first input a signal 110 provided at the output of the digital analog converter 102 relating to the amplitude component of the input signal 100, and, on the other hand, on a second input a signal 111 provided at the output of the phase modulator 104 relating to the phase component of the input signal 100.
The first and second inputs of the power amplifier may correspond respectively to the drain and gate inputs of this power amplifier.
Next, at the output of this power amplifier, a signal to be emitted 112 by the emission chain is thus obtained on the basis of the two signal components cited above.
Here, it may in particular be noted that a delay between these two components of the signal to be emitted may induce a degradation of the spectrum of this signal 112.
FIG. 2 provides another example of a part of an emission chain in which the signal to be transmitted is decomposed into two signal components according to a so-called “quadrature” decomposition.
This emission chain comprises a decomposition module 601 for decomposing a signal received at input, into first and second phase quadrature signal components, I and Q respectively. The signal is therefore represented in complex form, the real and imaginary parts forming the two quadrature components of the signal.
This decomposition module 601 exhibits a first output pathway which provides the first component I as input to a first digital/analog converter 602 and a second output pathway which provides the second component Q to a second digital/analog converter 603. At the output of these analog/digital converters, the first and second analog quadrature signal components are processed by an I/Q modulator 604 in such a way that they are transposed to the carrier frequency. After this modulation processing, the signal is then provided as input, or more precisely on the gate, of a power amplifier 105, the latter being suitable for providing a signal to be emitted.
In such an architecture, distortions may be induced by the digital/analog converters 602 and 603, as well as by the IQ modulator 604. These converters, this IQ modulator, with the different physical pathways traversed by the two analog components, may introduce a delay between the components I and Q in the signal obtained at the output of the IQ modulator.
A defect relating to poor balance (or “imbalance”) may also appear in this type of emission chain architecture, this defect being based on a difference between the gains of the two pathways I and Q.
A quadrature defect may also be detected, the signal components I and Q not being perfectly in quadrature.
The present invention aims to improve the situation in various cases, in particular such as those illustrated by the two examples described above.
An emission chain structure, such as that illustrated by the examples above, is known to the person skilled in the art. On the basis of the knowledge of this structure, it is advantageously possible to correct distortions which are inherent to this structure by virtue of a digital preprocessing. Such a digital preprocessing makes it possible to correct and to obtain at the output of the power amplifier of the emission chain, a radio signal corresponding to the signal that one wishes to transmit and exhibiting improved performance in particular as regards the distortion of the frequency spectrum.